This application is based on Japanese Patent Applications No. 11-263856 and No. 2000-83233 filed in Japan, the contents of which are incorporated hereinto by reference.
1. Field of the Invention
This invention relates to an encapsulant epoxy resin composition having superior laser markability, electrical properties, moldability, reliability and package surface appearance, and an electronic device having device components encapsulated with this composition.
2. Description of Related Art
With an improvement in integration of semiconductor device components such as ICs (integrated circuits) and LSIs (large-scale integrated circuits), device components are being made larger in its occupying area to a package and electronic devices such as semiconductor devices are being made smaller, thinner and more multiple-pin. Also, as electronic instruments are being made smaller in size and thickness, packaging methods have changed correspondingly, where the surface mount, which enables high-density packaging, has come into wide use rapidly in place of pin-insert type. In this surface mount, when electronic devices are mounted to a substrate, the electronic device themselves are exposed to a high temperature in a short time through the step of soldering at 200xc2x0 C. or above. At this time, the moisture contained in an encapsulant vaporizes and the vapor pressure thereby produced acts as a peel stress at the interface between the encapsulant and the device components or insert such as a lead frame to cause separation of the encapsulant from the insert at their interface. Especially in thin-type electronic devices, this leads to the occurrence of blistering or cracking of the electronic devices.
As measures for preventing the blistering or cracking caused by such separation, used are a method in which a coat material is applied on the device surface or the back of islands of a lead frame so as to improve its adhesion to the encapsulant, a method in which dimples or slits are formed on the back of islands of a lead frame, and a method in which a package is set up in LOC (lead on chip) structure so as to improve the adhesion to the encapsulant. These methods, however, have the problems that a high cost may result and no satisfactory effect can be attained. In addition, when the LOC structure is employed, the package surface may have a color non-uniformity to spoil surface appearance.
As another problem, the pitch between inner leads, between pads and between wires are being made narrower as electronic devices such as semiconductor devices are made smaller in size and more multiple-pin. Hence, where any conductive substance such as carbon black is present as large coarse particles in the encapsulant, such conductive particles may lie between inner leads, between pads, between wires or the like to cause faulty electrical characteristics. Accordingly, studies are made on using as colorants organic dyes, pigments or the like in place of carbon black (Japanese Patent Applications Laid-open KOKAI No. 63-179921 and No. 11-60904). These colorants, however, have problems of, e.g., a low YAG (yttrium aluminium garnet) laser markability, a low reliability and a high cost.
An object of the present invention is to provide an encapsulant epoxy resin composition having a superior moldability, that has superior laser markability and electrical properties, does not cause any short circuit due to conductive substances even in electronic devices such as semiconductor devices having narrow pitches between pads or between wires, and can obtain highly reliable packages without spoiling package surface appearance; and an electronic device having device components encapsulated with such a composition.
As a result of extensive studies, the present inventors have discovered that the above object can be achieved by mixing in an encapsulant epoxy resin composition a non-conductive carbon. Thus, they have accomplished the present invention.
The present invention provides an encapsulant epoxy resin composition comprising an epoxy resin, a curing agent, a non-conductive carbon and an inorganic filler. In the present invention, it is preferable to use a non-conductive carbon having an electrical resistance of 107 xcexa9 or above, and is preferable for the non-conductive carbon to be contained in an amount of from 0.1 to 10% by weight based on the total weight of the encapsulant epoxy resin composition.
The encapsulant epoxy resin composition has a good moldability and has a superior laser markability. Hence, using this composition, an electronic device having superior electrical properties, reliability and package surface appearance can be obtained. Accordingly, the present invention also provides an electronic device having an encapsulating member comprising a cured product of this encapsulant epoxy resin composition.